Spectroscope

ABSTRACT

A spectroscope is equipped with a temperature compensation mechanism that can reliably reduce a drift of a spectral image in the wavelength dispersion direction caused by a change in the environmental temperature irrespective of the form of the spectroscope. The spectroscope is provided with a first support member  17  that integrally supports an incidence member  11 , a collective optical system  13  and a detection element  15 , a second support member  21 , made of a material different from the first support member, that supports a wavelength dispersion element  14 , and a transmission member  24, 25  that transmits a contraction/expansion amount of the first support member to the second support member when environmental temperature changes. The second support member includes a deformation member  28  that elastically deforms, when environmental temperature changes, in accordance with a difference between its own contraction/expansion amount and the contraction/expansion amount of the first support member and a rotation member  26  that rotates minutely in accordance with elastic deformation of the deformation member. The said wavelength dispersion element is mounted on the rotation member in such a way that its wavelength dispersion direction is oriented perpendicular to the axial direction of the rotation member.

TECHNICAL FIELD

The present invention relates to a spectroscope that utilizes awavelength dispersion element such as a grating or a prism.

BACKGROUND ART

Spectroscopes utilizing a wavelength dispersion element have been widelyused in various fields such as physical analysis or chemical analysis.However, since the accuracy of wavelength measurement by a spectroscopeis likely to be unstable due to influence of a change in theenvironmental temperature, the environmental temperature is keptconstant in principle, when a spectroscope is used. As long as theenvironmental temperature is kept constant, a drift of a spectral imageof the light incident on the spectroscope in the wavelength dispersiondirection can be almost avoided and the accuracy of wavelengthmeasurement by the spectroscope can be made stable.

However, depending on the environment, it is sometimes difficult to keepa constant temperature. In view of this, in recent years it has beendesired to design spectroscopes in such a way that a spectral image willnot drift in the wavelength dispersion direction even if theenvironmental temperature changes. Most of spectroscopes equipped with atemperature compensation mechanism that have already been proposed use aconcave surface reflection type grating as a wavelength dispersionelement and a diode array as a detector for detecting a spectral image.

For example, Japanese Patent Application Laid-Open No. 8-254463 andJapanese Patent Application Laid-Open No. 9-218091 teach to reduce adrift of a spectral image due to a change in the environmentaltemperature by selecting the thermal expansion coefficient of a gratingholder and a casing in such a way as to match with the thermal expansioncoefficient of a diode array, and matching the shape of the gratingholder with the casing.

Furthermore, Japanese Patent Application Laid-Open No. 2000-298066 teachto reduce a drift of spectral images due to a change in theenvironmental temperature by inventively arranging the way of holding agrating and a diode array and optimizing a positioning structure for agrating holding member, a diode array holding member and a carrier.

However, the above-mentioned temperature compensation technologiesproposed in the prior art spectroscopes equipped with a temperaturecompensation mechanism are for exclusive use in spectroscopes that use aconcave surface reflectiion type grating as a wavelength dispersionelement and a diode array as a detector. Therefore, it is impossible toapply the above-described temperature compensation technologies tospectroscopes of other various types. If those technologies are appliedto a spectroscope of a different scheme by any means, the structure ofthe spectroscope will be complicated.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a spectroscope equippedwith a temperature compensation mechanism capable of reducing a drift ofspectral images in the wavelength dispersion direction due to a changein the environmental temperature reliably irrespective of the form ofthe spectroscope.

A spectroscope according to the first aspect of the present inventioncomprises an incidence member for introducing light to be measured, awavelength dispersion element for dispersing said light to be measuredfrom said incidence member in accordance with its wavelengths, acollective optical system that collects said light to be measured havingbeen dispersed by said wavelength dispersion element to form a spectralimage, and a detection element that detects said spectral image,characterized by that said wavelength dispersion element is adapted tobe rotatable, and a rotation mechanism for rotating said wavelengthdispersion element in accordance with a change in environmentaltemperature is provided so as to cancel a drift of said spectral imagein a wavelength dispersion direction caused by a change in environmentaltemperature.

Preferably, in the spectroscope according to the first aspect of thepresent invention, a reflective grating is used as said wavelengthdispersion element and a rotation amount Δa of said wavelengthdispersion element per 1° C. temperature change is expressed by thefollowing formula:Δa=Δs/f/(1+cos α/cos β),where Δs is a drift amount of said spectral image per 1° C. temperaturechange, f is the focal length of said collective optical system, α isthe incidence angle of the light to be measured incident on saidwavelength dispersion element, and β is the diffraction angle ofdiffracted light emergent from said wavelength dispersion element. Here,the angles α and β are measured from a normal line a grating surface ofsaid wavelength dispersion element as a reference.

A spectroscope according to the second aspect of the present inventioncomprises an incidence member for introducing light to be measured, awavelength dispersion element for dispersing said light to be measuredfrom said incidence member in accordance with its wavelengths, acollective optical system that collects said light to be measured havingbeen dispersed by said wavelength dispersion element to form a spectralimage, a detection element that detects said spectral image, a firstsupport member that supports said incidence member, said collectiveoptical system and said detection element integrally, a second supportmember, made of a material different from said first support member,that supports said wavelength dispersion element, and a transmissionmember that transmits a contraction/expansion amount of said firstsupport member to said second support member when environmentaltemperature changes, wherein said second support member includes adeformation member that elastically deforms, when environmentaltemperature changes, in accordance with a difference between thecontraction/expansion amount of said first support member transmittedfrom said transmission member and a contraction/expansion amount of saidsecond support member and a rotation member that rotates minutely inaccordance with elastic deformation of said deformation member, and

-   -   said wavelength dispersion element is mounted on said rotation        member in such a way that its wavelength dispersion direction is        oriented perpendicular to the axial direction of said rotation        member.

In a preferable mode of the spectroscope according to the second aspectof the present invention, rotation angle and rotation direction of saidrotation member upon change in environmental temperature are arranged inadvance so as to cancel a drift of said spectral image in the wavelengthdispersion direction.

In a preferable mode of the spectroscope according to the second aspectof the present invention, said second support member is a V-shapedmember in which two arm members are joined via said deformation memberof a thin form, one of said two arm members constituting said rotationmember, and said transmission member is a member that connects both endportions of said V-shaped member and said first support member andchanges the angle formed by said two arm members in accordance withcontraction/expansion of said first support member.

In a preferable mode of the spectroscope according to the second aspectof the present invention, the coefficient of linear expansion ρb of saidfirst support member, the coefficient of linear expansion ρm of saidsecond support member, the length y of one of said two arms, the lengthz of the other of said two arms and the angle a formed by said two armssatisfy the following formulas:Y/z={A±{square root}{square root over ( )}(A ²−4)}/2A=2 cos a+sin a·Δa/(ρb−ρm),

-   where Δa is the rotation angle of said rotation member that can    cancel a drift of said spectral image in the wavelength dispersion    direction per 1° C. environmental temperature change.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the overall structure of a spectroscope 10 according to anembodiment.

FIGS. 2A and 2B show the structure of a grating mount 16.

FIG. 3 illustrates a deformation of the grating mount 16.

EMBODIMENT OF THE INVENTION

In the following, an embodiment of the present invention will bedescribed in detail with reference to the drawings.

As shown in FIG. 1, a spectroscope 10 according to this embodiment iscomposed of an optical fiber 11, a mirror 12, a Littrow lens 13, agrating 14, a one-dimensional line sensor 15, a grating mount 16 and abase member 17. In addition, a light source that is not shown in thedrawing is provided in the upstream of the optical fiber 11. Among theoptical elements (11 to 15) that constitute the spectroscope 10, theoptical fiber 11, the mirror 12, the Littrow lens 13 and theone-dimensional line sensor 15 are disposed on the base member 17. Thegrating 14 is disposed on the grating mount 16, which is disposed on thebase member 17.

The spectroscope 10 of this embodiment is a spectroscope having atemperature compensation function, and it can be used under theenvironmental temperature range of −20° C. to +60° C.

Firstly, the structure and the function of the optical elements (11 to15) will be described, and subsequently the grating mount 16 and thebase member 17 will be specifically described.

The optical fiber 11 is a member (e.g. a single mode fiber) used forintroducing light to be measured from the light source (not shown) intothe interior of the spectroscope 10. The diameter of the optical fiberat the light emitting portion is, for example, 10 μm. The optical fiber11 corresponds to the “incidence member” recited in the claims.

The mirror 12 is an optical element for reflecting light to be measuredcoming from the optical fiber 11 to guide it to the Littrow lens 13.

The Littrow lens 13 has a lens having the function of collimating thelight to be measured L1 coming from the mirror 12 and the function ofcollecting diffracted light L3 (which will be described later) comingfrom the grating 14 to form a spectral image (the focal length of theLittrow lens being e.g. 50 mm). The light to be measured L2 collimatedby the Littrow lens 13 is guided to the grating 14, and the light to bemeasured L4 collected by the Littrow lens 13 is guided to theone-dimensional line sensor 15. The Littrow lens 13 corresponds to the“collective optical system” recited in the claims.

The grating 14 is a reflective planar diffraction grating in which alarge number of elongated grooves are arranged one-dimensionally. Thedirection in which the large number of grooves are arranged correspondsto the wavelength dispersion direction of the grating 14. The grating 14disperses the light to be measured L2 guided from the optical fiber 11by means of the mirror 12 and the Littrow lens 13 depending on thewavelength. The light to be measured after undergoing dispersion by thegrating 14 constitutes the aforementioned diffracted light L3. Thegrating 14 corresponds to the “wavelength dispersion element” recited inthe claims.

In this embodiment, the Littrow lens 13 and the grating 14 constitutes aboth side telecentric optical system. In other words, the grating isregarded as an aperture stop and it is disposed at a focal position ofthe Littrow lens 13.

The one-dimensional line sensor 15 has a light-receiving surface onwhich a large number of light receiving portions are arrangedone-dimensionally. The one-dimensional line sensor 15 is arranged insuch a way that the light receiving surface coincides with a focalposition of the Littrow lens 13 (i.e. the position at which a spectralimage is formed). The one-dimensional line sensor 15 is a detectionelement for detecting a spectral image formed by the Littrow lens 13.The direction in which the large number of light-receiving portions arearranged corresponds to the wavelength dispersion direction of thegrating 14.

The width in the wavelength dispersion direction of each light-receivingportion is designed in accordance with the wavelength resolutionrequired for detection of spectral images (for example, 25 μm). Thenumber of the light-receiving elements arranged on the light-receivingsurface of the one-dimensional line sensor 15 is designed in accordancewith the wavelength range required for detection of spectral images insuch a way that detection is made possible all through that wavelengthrange.

With the aforementioned optical elements (11 to 15), the light to bemeasured entering from the optical fiber 11 into the interior of thespectroscope 10 is collimated by the Littrow lens 13, then diffracted bythe grating 14 and then returning back to the Littrow lens 13 so as tobe collected. As a result, a spectral image is formed on thelight-receiving surface of the one-dimensional line sensor 15, and thespectral image is detected by the light-receiving portions arranged onthe light-receiving surface.

In the case that the light to be measured incident on the spectroscope10 is monochromatic light (light having a certain single wavelength),the spectral image will be of a spot-like shape substantially similar tothe light emitting portion of the optical fiber 11. In the case that thelight to be measured contains multiple types of light having differentwavelengths, the spectral image will be of a shape that extends alongthe wavelength dispersion direction. In some cases, a situation in whicha large number of spot-like spectral images are discretely arrangedalong the wavelength dispersion direction will occur.

If the spectral image drifts in the wavelength dispersion direction onthe light-receiving surface of the one-dimensional line sensor 15,measurement accuracy of the spectroscope 10 is deteriorated. Such adrift of the spectral image in the wavelength dispersion direction islikely to occur when the environmental temperature changes, and thefollowing reasons (1) to (5) are assumed to be principal contributingfactors for the drift.

(1) variation of the focal length of the Littrow lens 13; (2) variationof the refractive index of the air; (3) variation of the gratingconstant due to contraction/expansion of the grating 14; (4) positionalshift of the optical fiber 11 in the wavelength dispersion direction dueto contraction/expansion of the base member 17; and (5) rotation aboutthe groove line direction as the center.

However, among the above-mentioned factors (1) to (5), the factor (1),that is, variation of the focal length of the Littrow lens 13 can bereduced by optical design down to a small degree that does not matterpractically. The factor (2), that is, variation of the refractive indexof the air does not matter as long as the change in the environmentaltemperature is as small as about 100° C. In other words, even if theenvironmental temperature changes about 100° C., the degree of thewavelength variation of light in the air is negligible.

Consequently, the contributing factors to the drift of the spectralimage that should be practically taken into account are three factors,namely, (3) variation of the grating constant of the grating 14, (4)positional shift of the optical fiber 11 in the wavelength dispersiondirection, and (5) rotation about the groove line direction as thecenter.

In this embodiment, it is assumed that the spectroscope 10 is designedin such a way that when the environmental temperature rises from thelowest temperature (−20° C.) to the highest temperature (+60° C.) by 80°C., the spectral image will drift toward the shorter wavelength side by20 μm due to the aforementioned factors (3) and (4). In connection withthis, the shorter wavelength side is the direction indicated by arrow Bin FIG. 1.

The drift of the spectral image due to a change in the environmentaltemperature is substantially proportional to the change in thetemperature. Specifically, the drift amount Δs per 1° C. temperaturechange is 20 μm/80° C.=0.25 μm/° C. This drift amount is not negligibleas compared to the width (25 μm), in the wavelength dispersiondirection, of one light-receiving portion in the one-dimensional linesensor 15.

As mentioned before, in the case that the light to be measured incidenton the spectroscope 10 contains multiple types of light having differentwavelengths, the spectral image will be of a shape that extends alongthe wavelength dispersion direction, or a situation in which a largenumber of spot-like images are discretely arranged along the wavelengthdispersion direction will occur. Strictly speaking, the drift amountvaries slightly depending on the wavelength However, the variation isnegligibly small.

In view of this, it is assumed in this embodiment that among the lightsto be measured incident on the spectroscope 10, the light having awavelength in question (for example, the light of the centralwavelength) and the light having a wavelength in the neighborhood of thewavelength in question show the same behavior under a change in theenvironmental temperature. In other words, it is assumed that they driftby the same amount As (0.25 μm/° C.).

As described before, with a rise in the environmental temperature, thespectral image drifts toward the shorter wavelength side (in thedirection indicated by arrow B) by 0.25 μm/° C. due to theaforementioned factors (3) and (4). In addition, and the othercontributing factor to the drift of the spectral image is (5) rotationabout the groove line direction as the center, as also described before.

In the spectroscope 10 according to this embodiment, the grating 14 isrotated in such a way that the drift Δs (0.25 μm/° C. toward the shorterwavelength side) of the spectral image due to the aforementioned factors(3) and (4) is cancelled. The mechanism for rotating the grating 14 (thegrating mount 16 and the base member 17) will be described in detaillater.

When the grating 14 is rotated about the groove line direction (i.e. thedirection perpendicular to the plane of the drawing sheet of FIG. 1),diffracted light L3 emergent from the grating 14 is deflected, so thatthe spectral image drifts in the wavelength dispersion direction on thelight-receiving surface of the one-dimensional line sensor 15.

In connection with this, when the grating 14 is rotated in the directionin which the incidence angle α of the light to be measured L2 incidenton the grating 14 decreases (namely, the direction indicated by arrow Cin FIG. 1), the spectral image drifts toward the longer wavelength side(the direction opposite to the direction indicated by arrow B) with thisrotation. This is a drift that cancels the drift Δs caused by theaforementioned factors (3) and (4). The aforementioned incidence angle αis measured from the normal line 14 a of the grating 14.

Typically, the grating 14 is a reflective type, and in that case, therotation angle Δa of the grating that can cancel the drift Δs (=0.25μm/° C.) can be expressed by the following formula (1) using the focallength f of the Littrow lens 13, the incidence angle α of the light tobe measured L2 incident on the grating 14 and the diffraction angle β ofthe diffracted light L3 emergent from the grating 14, where thediffraction angle β is also measured from the normal line 14 a of thegrating 14.Δa=Δs/f/(1+cos α/cos β)  (1)

The above formula (1) is valid under the assumption that the wavelengthvariation of light within the air is negligible. The rotation angle Δaof the grating 14 is a rotation angle required per 1° C. temperaturevariation.

A specific rotation angle Δa calculated by the above formula (1) isΔa=2.76×10⁻⁶radian/° C., where values Δs=0.25 μm/° C., f=50 mm, α=70°,β=65° are used. The values of α and β are angles with respect to thelight having a wavelength in question (for example, the light having thecentral wavelength).

As per the above, when the environmental temperature changes, it ispossible to cancel a drift As of the spectral image caused by theaforementioned factors (3) and (4) by rotating the grating 14 by theaforementioned rotation angle Δa in the direction in which the incidenceangle α decreases (i.e. in the direction indicated by arrow C).

Next, the mechanism for rotating the grating 14 (i.e. the grating mount16 and the base member 17) will be described in detail. This mechanismis characterized by that it utilizes a difference in the coefficient oflinear expansion between the base member 17 and the grating mount 16.

The base member 17 integrally supports the optical fiber 11, the mirror12, the Littrow lens 13 and the one-dimensional line sensor 15. The basemember 17 corresponds to the “first support member” recited in theclaims. In this embodiment, the base member 17 is made of an aluminumalloy having a coefficient of linear expansion ρb (=24.3×10⁻⁶degree⁻¹).

When the environmental temperature changes, the base member 17 contractsor expands in accordance with its coefficient of linear expansion ρb. Inthis connection, the relative positional relationship of the opticalfiber 11, the mirror 12, the Littrow lens 13 and the one-dimensionalline sensor 15 disposed on the base member 17 changes isotropically withthe angular relationship being kept constant.

As shown in FIGS. 2A and 2B, the grating mount 16 is composed of aV-shaped member 21 for supporting the grating 14 and joint members 24and 25 for joining both end portions 22 and 23 of the V-shaped member 21with the base member 17. FIG. 2A is a top view and FIG. 2B is a sideview. In FIG. 2B, the portion corresponding to the V-shaped member 21 isrepresented by halftone dots.

In this embodiment, the grating mount 16 is made of an aluminum alloyhaving a coefficient of linear expansion ρm (=23.6×10⁻⁶degree⁻¹). TheV-shaped member 21 of the grating mount 16 corresponds to the “secondsupporting member” recited in the claims. The joint members 24 and 25correspond to the “transmission member”.

When the environmental temperature changes, the grating mount 16contracts or expands in accordance with its coefficient of linearexpansion ρm. Since the coefficient of linear expansion ρm of thegrating mount 16 differs from the coefficient of linear expansion ρb ofthe base member, the amount of contraction/expansion caused by a changein the environmental temperature is different between the grating mount16 and the base member 17.

Here, the V-shaped member 21 will be described in further detail.

The V-shaped member 21 is composed of two arm members 26 and 27 joinedby a thin deformation member 28 that can deform elastically. Inaddition, as described above, the V-shaped member 21 is joined with thebase member 17 at its both end portions 22 and 23 by means of the jointmembers 24 and 25 respectively. The end portions 22 and 23 of theV-shaped member 21 are thin deformation members that can deformelastically similar to the aforementioned deformation member 28.

Therefore, when the base member 17 contracts or expands with a change inthe environmental temperature in accordance with its coefficient oflinear expansion ρb, the contraction/expansion amount of the base member17 is transmitted to the V-shaped member 21 via the joint member 24 and25. Specifically, the distance between the joint members 24 and 25changes by an amount corresponding to the contraction/expansion of thebase member 17 and the distance between both end portions 22 and 23 ofthe V-shaped member 21 also changes.

Both end portions 22 and 23 of the V-shaped member 21 and thedeformation member 28 elastically deform in accordance with thedifference between their own contraction/expansion amount and thecontraction/expansion amount of the base member 17. All of these elasticdeformations are absorbed by a change in the bend angle. In addition,the arm members 26 and 27 of the V-shaped member 21 contract or expandin accordance with their own coefficient of linear expansion ρm.

Here, letting “I” be the center of one end portion of the V-shapedmember 21, “K” be the center of the other end portion 23 and “J” be thecenter of the deformation member 28, deformation of the V-shaped member21 caused by a change in the environmental temperature will beconsidered while focusing on the triangle IJK (shown in FIG. 3) obtainedby connecting the three centers I, J and K. In other words, deformationof the triangle IJK will be considered.

When the environmental temperature changes, the length of the side IK(i.e. the distance between both the end portions 22 and 23) of thetriangle IJK changes in accordance with the contraction/expansion amountof the base member 17. On the other hand, the length of the other twosides, namely the length of the side IJ (i.e. the length of the armmember 27) and the length of the side JK (i.e. the length of the armmember 26) change in accordance with the contraction/expansion amount ofthemselves or contraction/expansion amount of the V-shaped member 21.

Therefore, the triangle I′J′K′ after the change in the environmentaltemperature is not a similar figure to the original triangle IJK.Furthermore, the apex angle a′ (i.e. angle I′J′K′) is different from theapex angle a (i.e. angle IJK). In connection with this, the apex anglea′ and the apex angle a represent the bend angle of the deformationmember 28. The change in the bend angle of the deformation member (apexangle a→a′) is an elastic deformation.

Furthermore, when the apex angle a of the triangle IJK changes inaccordance with an elastic deformation of the deformation member 28, theangle formed by the two sides JK and JI (i.e. the arm member 26 and thearm member 27) that form the apex angle a changes. Consequently, thesides JK and JI rotate minutely. The axis of this minute rotation isperpendicular to the plane defined by the triangle IJK (i.e. the planeparallel to the plane of the drawing sheet).

In addition, the direction of minute rotation (rotation direction) ofthe side JK of the triangle IJK when the environmental temperature risescoincides with the direction indicated by arrow C in FIG. 1 (i.e. thedirection in which the incidence angle α decreases). This can beunderstood by considering the fact that its own coefficient of linearexpansion ρm is smaller than the coefficient of linear expansion ρb ofthe base member 17 and that the apex angle a of the triangle IJKincreases with an increase in the environmental temperature.

Therefore, the grating 14 is to be mounted on one arm member 26 of theV-shaped member 21 in such a way that the wavelength dispersiondirection is oriented in the direction perpendicular to the axialdirection (i.e. the direction perpendicular to the plane of the drawingsheet) of the arm member 26. Consequently, the groove line direction ofthe grating 14 becomes parallel to the axial direction of the arm member26.

The arm member 26 and the grating 14 are bonded by means of, forexample, an adhesive having elasticity so that deflection will not becaused by a difference in the coefficient of linear expansion of them.The arm member 26 of the V-shaped member 21 corresponds to the “rotationmember” recited in the claims.

The grating 14 mounted on the arm member 26 in this way always rotatesminutely about the groove direction of the grating 14 together with thearm member 26. In addition, when the environmental temperature rises,the grating 14 rotates minutely in the direction in which the incidenceangle α decreases (i.e. the direction indicated by arrow C).

The rotation angle Δa of the grating 14 that can cancel the driftΔs(=0.25 μm/° C.) of the spectral image caused by the aforementionedfactors (3) and (4), namely the rotation angle Δa required when theenvironmental temperature changes by 1° C. is expressed by formula (1)presented before, and the specific value of Δa is 2.76×10⁻⁶radian.

Therefore, if the arm member 26 of the V-shaped member 21 that supportsthe grating 14 is adapted to rotate by the aforementioned rotation angleΔa per 1° C. temperature change, the grating 14 will actually rotate bythe rotation angle Δa.

Letting Δa=a′−a (Δa: the rotation angle of the arm member 26 per 1° C.temperature change), the rotation angle Δa, the coefficient of linearexpansion ρb of the base member 17, the coefficient of linear expansionρm of the grating mount 16, the length y of the arm member 26 (or theside JK), the length z of the arm member 27 (or the side JI) and theangle a (or angle IJK) formed between the arms 26 and 27 satisfy thefollowing formulas (2) and (3).y/z={A±{square root}{square root over ( )}(A ²−4)}/2  (2)A=2 cos a+sin a·Δa/(ρb−ρm)  (3)

By substituting specific numerical values of the spectroscope accordingto this embodiment (a=90°, Δa=2.76×10⁻⁶radian, ρb=24.3×10 ⁻⁶degree⁻¹ andρm=23.6×10⁻⁶degree⁻¹) into formulas (2) and (3), the value of parameterA is obtained as A=3.94, and consequently, the ratio (y/z) of the lengthof the arm member 26 (or the side JK) and the length of the arm member27 (or the side JI) is obtained as y/z=3.67 (or 1/3.67).

It is possible to realize minute rotation the arm member 26 in thedirection indicated by arrow C by the aforementioned rotation angle Δaper 1° C. environmental temperature rise by determining the length y, zof the arm members 26 and 27 (or the sides JK and JI) based on theobtained result and arranging the V-shaped member 21 in such a way thatthe arm members 26 and 27 form an angle of 90°.

As a result, the grating 14 mounted on the arm member 26 also rotates inthe direction indicated by arrow C (i.e. the direction in which theincidence angle α decreases) by the aforementioned rotation angle Δa per1° C. environmental temperature rise. Therefore, the drift As (0.25 μm/°C. toward the shorter wavelength side) of the spectral image caused bythe aforementioned factors (3) and (4) can be canceled.

In the spectroscope 10 according to this embodiment, when theenvironmental temperature changes, the base member 17 and the gratingmount 16 (or the V-shaped member 21) contract or expand by differentamounts and the grating 14 minutely rotates by a predetermined angle inaccordance with the difference in the contraction/expansion amounts tocancel a drift of the spectral image in the wavelength dispersiondirection for sure. Consequently, it is possible to keep the position ofthe spectral image on the light-receiving surface of the one-dimensionalline sensor 15 at the same position even when the environmentaltemperature changes.

Thus, spectrum measurement of the light to be measured can be madepossible with stable measurement accuracy even when it is difficult tokeep the environmental temperature of the spectroscope 10 constant andthe environmental temperature changes in the range of −20° C. to +60° C.

In addition, since there is no need for particular environmentaltemperature control or provision of a environmental temperature controlfunction in the spectroscope 10, it is possible to realize aspectroscope 10 that is inexpensive and easy to use.

Furthermore, in the spectroscope 10 according to this embodiment, sincea one-dimensional line sensor 15 is used as an element for receivingspectral images, spectral images of multiple wavelengths can be receivedsimultaneously even in the state in which the grating 14 is fixed. Inother words, when the light to be measured contains multiple lights ofdifferent wavelengths, the intensity of the light to be measured can bemeasured easily on wavelength by wavelength basis.

Such a spectroscope 10 is preferably used in a wavelength divisionmultiplexing (WDM) optical communication system, as a device forseparating light emitted from a light source in the form of asemiconductor laser (a light source in which predetermined lights ofmultiple frequencies are multiplexed) (e.g. 1.5 μm band) and formonitoring the intensity characteristic of each frequency (i.e. awavelength monitor).

Generally, optical communication equipments are required to operateunder harsh environmental temperature conditions. When the spectroscope10 according to this embodiment is used as a wavelength monitor andmeasurement results obtained by the spectroscope 10 are fed back to thesemiconductor laser, it is possible to keep the intensity of the lightemitted from the semiconductor laser constant for each wavelength tothereby enable stable optical communication even if the environmentaltemperature changes.

Although the above embodiment has been described with reference to aspectroscope 10 that uses a reflective diffraction grating, the presentinvention can also be applied to a spectroscope that uses a transmissivediffraction grating. Furthermore, the present invention can also beapplied to a spectroscope that uses a single concave surface diffractiongrating in place of a planar diffraction grating and a Littrow lens.Still further, a collimating optical system and a collective opticalsystem may be separately provided in place of a single Littrow lens. Thecollimating optical system and the collective optical system may beeither dioptric systems or catoptric systems. Although a grating (i.e.diffracting grating) is used as a wavelength dispersion element, a prismmay also be used.

The present invention can be easily applied to any of theabove-mentioned various types of spectroscopes. Specifically, it ispossible to cancel a drift of spectral images in the wavelengthdispersion direction only by mounting a wavelength dispersion element ofa spectroscope on a rotation member similar to the above-described armmember 26. Therefore, the structure of a spectroscope provided with atemperature compensation function according to the present inventionwill not be made complex.

However, when a wavelength dispersion element is mounted on a rotationmember, the wavelength dispersion direction must be made perpendicularto the axial direction of the rotation member. In addition, it is alsonecessary to select various parameters such as the coefficient of linearexpansion ρm of a supporting member (corresponding to the V-shapedmember 21) that includes the rotation member and the coefficient oflinear expansion pb of a base member for supporting members (the opticalfiber 11 etc.) other than the wavelength dispersion memberappropriately. In addition, it is preferable to determine an optimumvalue for the rotation angle Δa of the wavelength dispersion elementrequired for temperature compensation, upon designing an individualspectroscope.

Although in the above-described embodiment a one-dimensional line sensor15 is used as an element for detecting a spectral image, an emissionslit and a detector may be used in place of the one-dimensional linesensor 15. The emission slit (detection element) has an elongatedaperture, which is disposed in such a way as to coincide with theposition at which the spectral image is formed. Thus, a partial image ofthe spectral image that has been transmitted through the aperture isreceived by the detector.

In that arrangement, lights having different wavelengths can be measuredby shifting the emission slit and the detector along the wavelengthdispersion direction or rotating the wavelength dispersion element aboutan axis perpendicular to the wavelength dispersion direction.Spectroscopes having such a structure is also preferably used as theaforementioned wavelength monitor in a wavelength division multiplexed(WDM) optical communication system.

Furthermore, although an optical fiber 11 is used as an incidence memberfor causing the light to be measured to enter the spectroscope 10, anincidence slit may also be used in place of the optical fiber 11. Theincidence slit has a single elongated aperture.

Although in the above-described embodiment, the Littrow lens 13 and thegrating 14 constitute a both side telecentric optical system, thepresent invention is not restricted to this feature. The presentinvention can also be applied to structures in which the Littrow lens 13and the grating 14 are out of telecentricity.

Although in the above-described embodiment, a reflective grating isused, the present invention can also be applied to structures that use atransmissive grating.

As has been described in the foregoing, the present invention canprovide a simple spectroscope equipped with a temperature compensationmechanism that can reliably reduce a drift of a spectral image in thewavelength dispersion direction caused by a change in the environmentaltemperature irrespective of the form of the spectroscope.

1-6. (canceled)
 7. A spectroscopic apparatus comprising: a wavelengthdispersion element on which light having one or more wavelengthcomponents is incident from an incidence member, for exertingspectroscopic effect on said light; a first support member that supportssaid wavelength dispersion element indirectly; and a second supportmember disposed between said wavelength dispersion element and saidfirst support member to connect said wavelength dispersion element andsaid first support member, wherein said second support member includes arotation member for rotating said wavelength dispersion element inaccordance with a difference in coefficient of linear expansion betweensaid first support member and said second support member inenvironmental temperature.
 8. A spectroscopic apparatus comprising: awavelength dispersion element on which light having one or morewavelength components is incident from an incidence member, for exertingspectroscopic effect on said light; a first support member that supportssaid wavelength dispersion element indirectly; a second support memberthat supports said wavelength dispersion element; and a transmissionmember disposed between said first support member and said secondsupport member to transmit a contraction/expansion amount of said firstsupport member to said second support member when environmentaltemperature changes, wherein said second support member includes adeformation member that elastically deforms, when environmentaltemperature changes, in accordance with a difference between thecontraction/expansion amount of said first support member transmittedfrom said transmission member and a contraction/expansion amount of saidsecond support member and a rotation member that rotates minutely inaccordance with elastic deformation of said deformation member.
 9. Aspectroscopic apparatus according to claim 8, wherein said secondsupport member comprises a V-shaped member in which two arm members arejoined via said deformation member of a thin form to form a V-shape as awhole, the angle formed by said two arm members being changed inaccordance with contraction/expansion of said first support member andsaid V-shaped member.
 10. A spectroscopic apparatus according to claim9, wherein coefficient of linear expansion ρb of said first supportmember, coefficient of linear expansion ρm of said second supportmember, length y of one of said two arm members, length z of the otherof said two arm members and angle a formed by said two arm memberssatisfy the following formulas:y/z={A±{square root}{square root over ( )}(A ²−4)}/2A=2 cos a+sin a·Δa/(ρb−ρm), where Δa is the rotation angle of saidrotation member that can cancel a drift of said spectral image in thewavelength dispersion direction per 1° C. environmental temperaturechange.
 11. A spectroscopic apparatus according to claim 7, furthercomprising a collective optical system that collects the light that hasundergone said spectroscopic effect to form a spectral image, whereinrotation angle and rotation direction of said rotation member arearranged in advance so as to cancel a drift of said spectral image inthe wavelength dispersion direction caused by change in environmentaltemperature.
 12. A spectroscopic apparatus according to claim 11,wherein said rotation member is adapted to cancel a drift of saidspectral image in the wavelength dispersion direction based on a driftamount of said spectral image relative to a change in environmentaltemperature that has been measured in advance for said spectroscopicapparatus without the rotation member.
 13. A spectroscopic apparatusaccording to claim 7, wherein said wavelength dispersion element ismounted on said rotation member in such a way that its wavelengthdispersion direction is oriented perpendicular to the axial direction ofsaid rotation member.
 14. A spectroscopic apparatus according to claim7, further comprising: an incidence member for causing light having atleast one wavelength to enter said wavelength dispersion element; and acollimating optical system for collimating light from said incidencemember to cause the light to enter said wavelength dispersion element,wherein said incidence member and said collimating optical system aresupported by said first support member.
 15. A spectroscopic apparatusaccording to claim 14, further comprising: a collective optical systemfor collecting light that has undergone spectroscopic effect by thewavelength dispersion element to form a spectral image; and a lightreceiving element for receiving said spectral image, wherein saidcollective optical system and said light receiving element are supportedby said first support member.
 16. A spectroscopic apparatus according toclaim 15, wherein said collimating optical system and said collectiveoptical system include at least one common lens.
 17. A spectroscopicapparatus according to claim 15, wherein said light receiving elementcomprises a one-dimensional line sensor.
 18. A spectroscopic apparatusaccording to claim 15, wherein said light receiving element comprises aplurality of light receiving portions arranged on a surface on which thespectral image is formed by the collective optical system, and lightincident on each light receiving portion has a different wavelength. 19.A spectroscopic apparatus according to claim 8, further comprising acollective optical system that collects the light that has undergonesaid spectroscopic effect to form a spectral image, wherein rotationangle and rotation direction of said rotation member are arranged inadvance so as to cancel a drift of said spectral image in the wavelengthdispersion direction caused by change in environmental temperature. 20.A spectroscopic apparatus according to claim 19, wherein said rotationmember is adapted to cancel a drift of said spectral image in thewavelength dispersion direction based on a drift amount of said spectralimage relative to a change in environmental temperature that has beenmeasured in advance for said spectroscopic apparatus without therotation member.
 21. A spectroscopic apparatus according to claim 8,wherein said wavelength dispersion element is mounted on said rotationmember in such a way that its wavelength dispersion direction isoriented perpendicular to the axial direction of said rotation member.22. A spectroscopic apparatus according to claim 8, further comprising:an incidence member for causing light having at least one wavelength toenter said wavelength dispersion element; and a collimating opticalsystem for collimating light from said incidence member to cause thelight to enter said wavelength dispersion element, wherein saidincidence member and said collimating optical system are supported bysaid first support member.
 23. A spectroscopic apparatus according toclaim 22, further comprising: a collective optical system for collectinglight that has undergone spectroscopic effect by the wavelengthdispersion element to form a spectral image; and a light receivingelement for receiving said spectral image, wherein said collectiveoptical system and said light receiving element are supported by saidfirst support member.
 24. A spectroscopic apparatus according to claim23, wherein said collimating optical system and said collective opticalsystem include at least one common lens.
 25. A spectroscopic apparatusaccording to claim 23, wherein said light receiving element comprises aone-dimensional line sensor.
 26. A spectroscopic apparatus according toclaim 23, wherein said light receiving element comprises a plurality oflight receiving portions arranged on a surface on which the spectralimage is formed by the collective optical system, and light incident oneach light receiving portion has a different wavelength.